Surface protrusion induced by inter-diffusion on Cu-Sn micro-pillars

Yang Chen; Wenjie Dai; Yingxia Liu; Chih Chen; K.N. Tu; Guang Chen

Materials & Design (Dec 2022)

Surface protrusion induced by inter-diffusion on Cu-Sn micro-pillars

Yang Chen,
Wenjie Dai,
Yingxia Liu,
Chih Chen,
K.N. Tu,
Guang Chen

Affiliations

Yang Chen: Dept. of Materials Science and Engineering, Uni. of California, Los Angeles, CA 90095-1595, USA; MIIT Key Laboratory of Advanced Metallic and Intermetallic Materials Technology, Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, China
Wenjie Dai: MIIT Key Laboratory of Advanced Metallic and Intermetallic Materials Technology, Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, China
Yingxia Liu: Dept. of Materials Science and Engineering, Uni. of California, Los Angeles, CA 90095-1595, USA
Chih Chen: Dept. of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan, ROC
K.N. Tu: Dept. of Materials Science and Engineering, Uni. of California, Los Angeles, CA 90095-1595, USA; Dept. of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan, ROC; Corresponding authors at: Dept. of Materials Science and Engineering, Uni. of California, Los Angeles, CA 90095-1595, USA (K.N. Tu).
Guang Chen: MIIT Key Laboratory of Advanced Metallic and Intermetallic Materials Technology, Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing 210094, China; Corresponding authors at: Dept. of Materials Science and Engineering, Uni. of California, Los Angeles, CA 90095-1595, USA (K.N. Tu).

Journal volume & issue: Vol. 224
p. 111318

Abstract

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With downward scaling of the micro-bumps in three-dimensional integrated circuits, surface inter-diffusion becomes dominant, changing the kinetic path of intermetallic compounds (IMC) formation and causing serious reliability issues. However, an in-depth understanding of the surface inter-diffusion process and the corresponding influence on the formation mechanism of IMC in a micro-bump remain unclear. We conducted annealing at 170 ℃, over 16 h for pillar type Sn/Cu micro-bumps and observed a unique 2-step sidewall Cu3Sn IMC formation phenomenon on the FIB-cut clean surface of the micro-bumps. It is found the two-step sidewall IMC formation is dominated by the surface inter-diffusion of Sn and Cu atoms. Density functional theory calculations reveal that the activation energy barrier of nucleation for sidewall Cu3Sn IMC is about 1/3 of that of sidewall Cu6Sn5 on corresponding interfacial IMC layers, making the formation of sidewall Cu3Sn dominant. Moreover, we proposed a kinetic model that can predict the mean lateral growth rate of the sidewall IMC which may cause fatal short-circuit failure.

Published in Materials & Design

ISSN: 0264-1275 (Print); 1873-4197 (Online)
Publisher: Elsevier
Country of publisher: United Kingdom
LCC subjects: Technology: Electrical engineering. Electronics. Nuclear engineering: Materials of engineering and construction. Mechanics of materials
Website: https://www.journals.elsevier.com/materials-and-design

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